UPDATED — August 6, 4:19 a.m. ET

JUJA, Kenya — A 19-year-old Oklahoma man has been indicted for allegedly sexually assaulting children on his most recent trip to volunteer in Kenya.

Matthew Lane Durham of Edmond, Okla., was charged in U.S. District Court on July 18 with assaulting between 4 and 10 children, ages four to nine, at Upendo Children’s Home in Juja, Kenya, about an hour outside of the capital, Nairobi. He is expected to appear in court on Monday for a bail hearing.

The alleged assaults occurred some time between April 30 and June 17, according to the FBI.

This was Durham’s fourth volunteer trip to the children’s home, which was founded two years ago by dual Kenyan-U.S. citizen Eunice Menja, also of Edmond. The home is in a poor rural community a 20-minute drive, along bumpy dirt roads through flat, empty fields, from Juja town.

Menja declined repeated requests, in person and by email, for comment and referred BuzzFeed to an FBI affidavit.

According to that affidavit, this fourth volunteer visit was the first time Durham requested to lodge in the same compound as the children, in an “overflow bunk.” The affidavit states that the caretaker of the children’s home in early June noticed Durham acting “odd” — lying next to the children late at night or embracing them in what she characterized as a “lingering” manner. The FBI alleges that the caretaker asked some children about this and that they told her Durham had touched them sexually.

The caretaker, who is Menja’s sister, told Menja about the children’s allegations. On June 12, Menja confronted Durham, who denied the accusation but allegedly admitted to “struggling with homosexuality and child pornography,” according to the FBI.

Menja took Durham’s passport. Five days later, he allegedly confessed to the assaults. The FBI states that Menja took a partial video of his confession with her cell phone and that, at her request, he also wrote in detail the acts he allegedly committed against each child.

Menja took the so-called confessions to the local Juja police station and asked police to hold Durham in Kenya while they investigated, an officer familiar with the case told BuzzFeed.

Police said they informed Menja that they could not hold Durham without independently investigating the allegations, and that Menja could not lawfully retain his passport. Menja returned Durham’s passport, and he left the country.

Menja also forwarded the alleged confessions to the U.S. Embassy, according to the affidavit. The embassy declined to take questions on the matter.

Menja’s personal Facebook page makes several references to the situation, without specifics, including a post on June 30 that says, “Road to healing #1: Our kiddos at Upendo Children’s Home have started receiving counseling.”

Durham’s lawyer, Stephen Jones, says that the FBI affidavit — so far the only public information about the allegations — contains “several critical errors.” Jones also says that Durham wrote out “the so-called confession” and was recorded on Menja’s cell phone under coercion.

Jones disputes the FBI’s statement that Durham voluntarily surrendered his passport to Menja; Jones says it was taken from Durham. Jones also disputes that Durham was the only member of the mission trip to stay in the “overflow” bunk.

“His mother was there until four days before” he was accused of assault, Jones said. “She stayed in the bunkhouse.”

Durham’s mother, Melissa, had organized supplies and donations for Upendo several times. On a May 23 post to the Facebook page of Upendo Kids, Menja praised Melissa Durham’s help.

“We have all served as volunteers at Upendo, but Melissa’s level of commitment towards our 2014 mission trip school supplies and stuff (from at least 4 schools) broke the record today. I am not sure how she does it each year, but I am proud to be travelling with Melissa to Kenya (once gain)As if that is not enough, Melissa also gave birth to a wonderful man of God, Matthew Durham and I don’t think she knew that she was raising her son so that he could dedicate all his summers and major holidays to the children of Kenya.”

Durham responded: “Eunice, I’m just so thankful that you started Upendo Kids and give so much back to the precious people in your country! And I’m thankful that you have given my son a place to serve!:)”

Four days after Durham’s mother left, on June 12, Jones says that Durham “was filed into a room and confronted by five or six people, some of them volunteers, some of them staff, some members of the family [that runs the home], accusing him of inappropriate behavior with orphans. He denied it,” Jones said.

Jones alleges that Durham called his parents at Menja’s request and that Menja informed them she “would not let him leave the country” until he confessed. Jones said that Durham was asked, “‘What are you going to do for my girls? What are you going to do for my girls?’ They [Menja and staff] didn’t specifically ask for money but in Matthew’s mind that was the inference,” Jones said.

Jones said that in a call with both of his parents, Durham’s mother advised him to “‘say whatever you need to say, write whatever they want you to write, get out of the country now.’”

Durham wrote and signed statements on June 17. Jones said Durham never spoke with anyone from the U.S. Embassy in Nairobi between June 12 and 17. He also never spoke with anyone who identified themselves as a Kenyan police officer, Jones added.

Police in Juja said that by the time they began their investigation, Durham had already left the country.

Police said they spent approximately one month investigating the allegations, including medical examinations. Doctors documented “broken hymens” in five of the six girls alleged to have been abused, according to Kenyan police. (Forensic medical professionals say that it is impossible to estimate the date of injuries in sexual assaults that have occurred two or more weeks before an examination.)

The investigating officer forwarded the case file to Kenya’s director of public prosecutions, the U.S. Embassy, and Interpol, police said.

U.S. federal law gives American courts jurisdiction over certain sex crimes committed by citizens against minors abroad.

Durham could proceed to trial as early as September, according to the district attorney’s office.

Jina Moore is the international women's rights correspondent for BuzzFeed News and is based in Nairobi. Moore has reported from Liberia at the height of the Ebola crisis and on women’s issues around the world.